Effect of active alkali and alkaline earth metals on the reactivity of co-gasification char from coal and corn straws

Abstract

To evaluate the effect of active alkali and alkaline earth metals (AAEMs) on the co-gasification process, this work studied the gasification/oxidation/combustion reactivity of co-gasification chars acquired at different gasification times by four mixtures: raw coal and raw corn straws (RSM + RCS), acid-washing coal and raw corn straws (HSM + RCS), raw coal and acid-washing corn straws (RSM + HCS), and acid-washing coal and acid-washing corn straws (HSM + HCS). The results indicate that the char contents of the raw/acid-washed samples and mixed samples in the first 5 min of gasification are mainly affected by influence-1 (active AAEMs promote the increase of the char contents during pyrolysis). And after gasification for 10 min, influence-2 (active AAEMs catalyze the reaction of char, resulting in the reduction of char content during gasification) occupies the core position. The order in the effect of active AAEMs on gasification reactivity of char is active AAEMs in RSM and RCS > active AAEMs in RCS > active AAEMs in RSM > no active AAEMs. Among them, the effects of active AAEMs in RCS and active AAEMs in RSM and RCS are very significant. Besides, the ratios of experimental value to theoretical value of residual carbon contents for RSM + RCS chars and HSM + RCS chars range from 19 to 57%, while those for RSM + HCS chars and HSM + HCS chars range from 96 to 103% during oxidation reaction. Active AAEMs in RCS have a significant catalytic effect on oxidation/combustion reactivity of char. The maximum oxidation rate of RCS char is 314 times higher than that of HCS chars. The maximum combustion rate of RCS chars is 15–20 times higher than that of HCS chars. However, the maximum oxidation/combustion rate of RSM chars is less than 2 times that of HSM chars.